The broad, long-term objective is to understand the mechanisms by which organisms control transition metal ions and the roles of these metals, particularly copper, in cell signaling and regulatory pathways. Copper homeostasis is of major importance to human health, yet the pathways for intracellular copper trafficking are unclear, and relatively few components in copper sensing and trafficking have been identified. This proposal focuses on RTE, a previously undescribed gene of novel sequence, which is hypothesized to encode a sensor, transporter or chaperone for copper. The RTE gene is highly conserved, and is present in a single copy in animals and in two copies in plants. The aim of this proposal is to define the role of RTE in metal homeostasis. The studies will center primarily on the RTE1 gene of the model plant Arabidopsis thaliana. Genetic analyses in Arabidopsis have linked RTE1 to two copper-binding proteins in ethylene signal transduction. One is the copper-requiring ethylene receptor ETR1, whose function is dependent on RTE1. The other is RAN1, a homolog of the human Menkes/Wilson's P-type ATPase copper transporter, which is likewise required for ethylene receptor function. Investigating the genetic and cellular basis for these connections to RTE1 in Arabidopsis will utilize powerful genetic tools for understanding the cellular roles of RTE. Parallel experiments with respect to RTE and the Menkes/Wilson's homolog CUA-1 will be performed in the animal genetic model Caenorhabditis elegans, allowing comparison and integration of results from an animal system with those in plants. Saccharomyces cerevisiae and mammalian cell culture will be employed for ethylene binding assays and copper binding assays, respectively. The proposed experiments will use a combination of molecular genetics, cell biology and biochemical methods. The elucidation of RTE function should have a direct impact on understanding the processes of metal homeostasis for the benefit of human health.